The present invention relates to an irrigation-aspiration apparatus for typical use in cataract surgery which involves the extraction of an opaque lens due to cataract.
An irrigation-aspiration apparatus is known that supplies an irrigating fluid into the eyeball and which removes through aspiration the supplied irrigating fluid together with the tissue to be stripped from within the eyeball. This apparatus is typically used in cataract surgery which involves the extraction of an opaque lens due to cataract. Primarily for the reason of creating only a small incision wound, an ultrasonic phacoemulsification and aspiration technique using a spallation handpiece which operates under ultrasonic vibrations (hereunder referred to as an "US handpiece") is commonly practiced today in cataract surgery.
In this method of surgery, ultrasonic vibrations are applied to the tubular spallation tip having an aspiration hole at the distal end of the US handpiece so as to spall and emulsify the nucleus in the lens. During the operation, an irrigating fluid flowing through an irrigation tube is supplied into the eyeball from a site near the distal end of the spallation tip. The nuclei spalled and emulsified in smaller particles by the ultrasonic vibrations applied to the spallation tip is given an aspirating pressure by the aspirator so that it is drawn in through the aspiration hole at the distal end of the spallation tip together with the intraocularly supplied irrigating fluid and thereafter drained to the outside of the eyeball. A peristaltic pump is known as the aspirator which imparts the aspirating pressure.
As shown in FIG. 4, a peristaltic pump comprises a plurality of rollers 21' spaced apart on the same circumference of a rotating support 22' which revolves to cause the rollers 21' to compress an aspirating tube 16' to collapse on a tube receptacle 25' as they rotate. As a consequence, the fluid (aspirated liquid or air) flowing through the tube 16' is pushed out in the direction of rotation of the rollers 21', thereby creating an aspirating pressure.
A problem with the peristaltic pump shown in FIG. 4 is that when the rollers 21' start to compress the aspirating tube 16' to collapse, a portion of the fluid in the aspirating tube 16' (as indicated by volume A') will flow back. This produces periodic fluctuations in aspiration called "pulsation" which, in turn, causes pressure variations in the eye under operation, occasionally making it difficult to achieve correct control in the aspirating pressure and the rate of inflow.